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SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE 



VOL. 35 



medullary canal and form the dividing partition. Four large vascular canals 

 appear in the anterior wall and two or three in the posterior. Their lacuna? 

 are long and oval with long and straight canaliculi. 

 Type I-III, Ic. 



FEMUR OF GALLUS. DOMESTIC CHICKEN. CB. MED. COLL. 



Pl. 7, Fig. 104. Syn. Tab. Ill 



Antero-posterior diameter of bone, 9 mm. ; lateral, 9 mm. 

 Antero-posterior diameter of medullary canal, 7 mm. ; lateral, 7 mm. 

 The medullary canal is full. Medullary index, 153%. 



Structure. — Well marked external circumferential lamella? with long, nar- 

 row lacunae and branching canaliculi surround the section. The central ring is 

 composed of irregularly shaped Haversian systems of the (Ic) differentiation. 

 At the posterior ridge they occupy the entire thickness of the wall of the bone 

 as far as the internal circumferential lamella?. Interspersed between the sys- 

 tems are short lamella?. 



Internal circumferential lamella? completely surround the medullary canal. 

 Their lacuna? are long and narrow and their canaliculi are bushy. 



Type I-III, Ic. 



FEMUE OF COEVUS AMEBICANUS. CBOW. CB. MED. COLL. 



Pl. 7, Fig. 105. Syn. Tab. Ill 



Antero-posterior diameter of bone, 4 mm. ; lateral, 3 mm. 

 Antero-posterior diameter of medullary canal, 2.5 mm. ; lateral, 2 mm. 

 The medullary canal is full. Medullary index, 70%. 



Structure. — External circumferential lamella? form a wide ring around the 

 bone. The lacuna? are oval with bushy, connecting canaliculi. 



The central ring is composed of lamella? and irregular Haversian systems 

 of the (Ic) stage of development. There is very little difference in the struc- 

 ture of the various parts of the bone. 



Internal circumferential lamella? form a narrow ring around the medullary 

 canal. Their lacuna? are narrow and long and their canaliculi are long and 

 branching. 



Type I-III, Ic. 



FEMUR OF ASIO WILSONIANUS. LONG-EARED OWL 



Pl. 7, Fig. 106. Syn. Tab. Ill 



Antero-posterior diameter of bone, 8 mm. ; lateral, 7 mm. 

 Antero-posterior diameter of medullary canal, 6 mm. ; lateral, 6 mm. 

 The medullary canal is full. Medullary index, 178%. 



